Reversing rolling mills, herein referred to generically as "Steckel mills" operate in conjunction with a pair of coiler furnaces, one immediately upstream of the Steckel mill and one immediately downstream of the Steckel mill. Once the strip being rolled by the Steckel mill is of a thickness sufficiently small to be coiled within the coiler furnace, the leading edge of the strip is directed into the entrance/exit port or mouth of the collet furnace and wound up on the collet furnace drum. Conventionally, the trailing edge of the strip is stopped as close to the Steckel mill as possible so that rolling in the reverse direction can be commenced with as short a turnaround time as possible.
On the reverse reduction rolling of the strip, the strip is paid out of the coiler furnace from the drum via the entrance/exit port. On the initial payout, the strip is driven longitudinally by a pair of pinch rolls typically located between the coiler furnace and the Steckel mill in close proximity to the Steckel mill.
The purpose of the coiler furnace is, of course, to try to keep the temperature of the strip sufficiently high to enable the strip to be rolled successfully, and to obtain the desired metallurgical properties in the finished product. It is considered important under conventional practice to minimize the turnaround time between the reversal of direction of rolling so that the temperature drop in the strip being rolled is not unacceptable.
A problem with the conventional practice is that the leading and trailing edge portions of the strip enter the coiler furnace only on alternate passes and, therefore, are subject to more severe temperature drop than the intermediate portions of the strip which are within a coiler furnace for at least part of the time during each pass through the Steckel mill and into a coiler furnace. It is thus easier to maintain the intermediate portions of the strip at an acceptably high temperature than it is to maintain the leading and trailing ends of the strip at an acceptably high temperature. The problem is significant because the distance between the Steckel mill and the coiler furnace port may be as much 30 feet. The leading and trailing ends of the strip that enter the coiler furnaces only on alternate passes combined, therefore, may total as much as about 60 feet of the total length of the strip. This can be a significant portion--as much as ten percent or even somewhat higher--of the total length of the final coiled strip product. Depending upon customer requirements, the leading and trailing end pieces must frequently be severed from the coil before it is cut for shipment because of the failure of the leading and trailing ends to meet dimensional or metallurgical specifications. The leading and trailing end pieces cut off are essentially scrap steel that must be reprocessed entirely to be of any commerical value, and this adds appreciably to the cost per ton of the finished coil product being produced by the Steckel mill.